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-rw-r--r--mm/vmscan.c19
1 files changed, 17 insertions, 2 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 53e4534885ad..5a8776eb0f43 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1439,6 +1439,19 @@ putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
}
/*
+ * If a kernel thread (such as nfsd for loop-back mounts) services
+ * a backing device by writing to the page cache it sets PF_LESS_THROTTLE.
+ * In that case we should only throttle if the backing device it is
+ * writing to is congested. In other cases it is safe to throttle.
+ */
+static int current_may_throttle(void)
+{
+ return !(current->flags & PF_LESS_THROTTLE) ||
+ current->backing_dev_info == NULL ||
+ bdi_write_congested(current->backing_dev_info);
+}
+
+/*
* shrink_inactive_list() is a helper for shrink_zone(). It returns the number
* of reclaimed pages
*/
@@ -1566,7 +1579,8 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
* implies that pages are cycling through the LRU faster than
* they are written so also forcibly stall.
*/
- if (nr_unqueued_dirty == nr_taken || nr_immediate)
+ if ((nr_unqueued_dirty == nr_taken || nr_immediate) &&
+ current_may_throttle())
congestion_wait(BLK_RW_ASYNC, HZ/10);
}
@@ -1575,7 +1589,8 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
* is congested. Allow kswapd to continue until it starts encountering
* unqueued dirty pages or cycling through the LRU too quickly.
*/
- if (!sc->hibernation_mode && !current_is_kswapd())
+ if (!sc->hibernation_mode && !current_is_kswapd() &&
+ current_may_throttle())
wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,